Mushrooms are a familiar sight, often appearing after a rainstorm. The visible part is only one small component of a much larger organism. A mushroom is not a plant, as it lacks chlorophyll and cannot perform photosynthesis. It belongs to the Kingdom Fungi, a distinct biological group that obtains nourishment through a fundamentally different process than plants or animals. The entire living body of the fungus is actually hidden from view, extending beneath the surface in a vast, interconnected structure.
The Hidden Network: Mycelium
The main body of the fungus is an intricate network called the mycelium. This vegetative structure is composed of numerous microscopic filaments known as hyphae, which are thin, thread-like strands. The hyphae branch out extensively, forming a dense, web-like mass that permeates the substrate, often the soil, decaying wood, or leaf litter beneath the surface.
The mycelium acts as the fungal equivalent of roots, though its function is more complex than simple anchoring and water uptake. The mycelium aggressively colonizes its environment, sometimes spreading for many square miles in a single organism. In fact, just a small amount of fertile soil can contain up to a kilometer of these fine mycelial filaments. The mycelium remains active and growing throughout the year, even when no mushrooms are visible above ground.
The primary function of the mycelium is to absorb nutrients from its surroundings. It possesses an extremely high surface-area-to-volume ratio, which is ideal for this absorption process. The unseen network is continuously searching for and consuming organic matter within the ground to fuel the fungus’s growth and eventual reproduction.
The Role of the Fruiting Body
The familiar structure people call a mushroom is the fruiting body, which is the reproductive organ of the fungus. This structure is temporary and appears only when environmental conditions, such as temperature and moisture, are suitable for reproduction.
The sole purpose of the fruiting body is to produce and disperse spores. These spores are typically housed in specialized structures, such as the gills or pores found underneath the cap. The fruiting body emerges above the ground to facilitate this dispersal, allowing the spores to be carried away efficiently by air currents or animals.
The energy and materials required to construct this visible, short-lived structure are channeled from the extensive underground mycelial network. The appearance of the fruiting body signals the transition of the fungus from its vegetative, feeding stage to its reproductive phase. After releasing its spores, the fruiting body quickly decays, leaving the mycelium to continue its work in the substrate below.
How Fungi Get Their Food
Fungi are heterotrophs, meaning they cannot produce their own food like plants through photosynthesis. Instead, they obtain their energy by breaking down organic compounds that are already present in their environment.
Most fungi are saprotrophs, acting as the primary decomposers in many ecosystems. They feed on non-living organic material, such as dead leaves, fallen branches, animal waste, and the dense cellulose and lignin found in wood. To access the nutrients locked inside this complex matter, the mycelium secretes powerful digestive enzymes directly into the substrate.
This process is known as external digestion, where the large organic molecules are broken down into smaller, soluble compounds outside the fungal body. The hyphae then absorb these simpler molecules, like sugars and amino acids, through their cell walls. The ground or substrate, therefore, functions as the fungus’s external stomach.